Stylocheilus longicauda (Quoy & Gaimard, 1824)

Yonow, Nathalie, 2012, Opisthobranchs from the western Indian Ocean, with descriptions of two new species and ten new records (Mollusca, Gastropoda), ZooKeys 197, pp. 1-130 : 10-11

Stylocheilus longicauda (Quoy & Gaimard, 1824) Plate 13

Aplysia longicauda Quoy & Gaimard, 1824: 421, pl 66 Fig. 8 (New Guinea); Rang 1828: 73, pl. 22 figs 8 - 10 (Quoy & Gaimard specimen, on “fucus”).

Aplysia citrina Rang, 1828: 71, pl. 22 figs. 1, 2 (Atlantic Ocean on Sargassum ).

Aplysia nudata Rang, 1828: 72, pl. 22 figs. 3-5 (Sandwich Islands on “fucus”).

Aplysia striata Quoy & Gaimard, 1832: 315 (New Guinea).

Stylocheilus longicauda . - Bebbington 1974: 87, figs. 7G, 14, 15 (Kenya and Zanzibar); Gosliner 1987: 49, fig. 30 (South Africa); Yonow and Hayward 1991: 5, fig. 3E (Mauritius); Yonow 2008: 104 (Red Sea).

Stylocheilus striatus . - Yonow 2008: 108 (Red Sea); Apte 2009: 167, fig. 1k (Laccadive Islands); Richmond 2011: 278 (East Africa).

Material.

Maldives: 6 mm in length pres., 2 m depth on algal-covered stone, Kuredu, Lhaviyani Atoll, 10-24 March 1998, leg. J Hinterkircher; three specimens collected of many, 50-70 mm live lengths (28-32 mm preserved), on algae growing on floating grouper cage near surface, Kiadhu Tila, Felidhoo Atoll, 23 July 1994, leg. RC Anderson (striations still visible on preserved specimens). - Zanzibar: numerous specimens 10-50 mm pres. lengths, Mazzini, intertidal and low water forming chains on sand and rocks in sea grass beds, 09 September 1993, leg. MD Richmond (numerous villi, very long rhinophores and oral tentacles). - Mauritius, La Réunion, Mayotte, and Madagascar: photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm. - Oman: Muscat, 01-12 April 2009, photos of several individuals, S Kahlbrock.

Description/Distribution.

Benthic form of this circumglobal species distinguished by fine longitudinal brown-to-black lines usually interrupted by ‘eyespots’ with bright blue centres; tail long, swelling present in middle of body where parapodial lobes enclose large gill and anal siphon; rhinophores and oral tentacles long and slender. Specimens in any given population may have few or numerous villi, and this variation is still visible in the preserved material. It can be locally common in sea grass beds and shallow water, especially during the breeding season, but this does not happen every year (P Bidgrain, pers. comm. and http://seaslugs.free.fr/nudibranche/a_intro.htm).

Remarks.

There is probably only one species of Stylocheilus occurring in two forms, the benthic striated form described and illustrated here, which was known as striatus, and the yellow pelagic form associated with seaweeds currently known as longicauda.

This may be an appropriate location to discuss the problems posed by the aplysiids distributed in the Indo-West Pacific: all species covered in this work are complex and appear to comprise colour forms identified as separate species, as well as having different habitat preferences. Aplysia parvula occurs consistently in at least two forms, the larger pale-coloured shallow water one associated with algae and the tiny black reef form although other colour forms are recorded (http://seaslugs.free.fr/nudibranche/a_intro.htm and http://www.nudipixel.net/species/aplysia_parvula/). It is noted that the radulae and shells were similar, with slight differences. Dolabrifera dolabrifera has been described under many names but has long been recognised as a single species. Many species of Dolabella have been described but were historically resolved to two species, with different external and (possibly) internal morphologies and shells; these are synonymised as one species in this work. The history of Stylocheilus is also complicated, with two very different forms inhabiting very different environments. Clearly the aplysiids are in need of revision, entailing comparison of specimens from different regions and habitats as well as a very thorough review of the literature; it is probable that the numerous species names currently listed will dissolve into fewer, variable species.